Shrinkage resistant auto exhaust catalysts

ABSTRACT

A shrinkage resistant auto exhaust catalyst comprised of an alumina support and specified amounts of copper, chromium, and specified rare earth compounds, and the use of the catalysts under oxidizing conditions to oxidize carbon monoxide and hydrocarbons in exhaust.

United States Patent m Roth et al. May 13, 1975 SHRINKAGE RESISTANT AUTOEXHAUST CATALYSTS [56] References Cited [75] inventors: James F. Roth,St. Louis; James W. TED TATE PATENTS Gambell, Creve Coeur; Charles R.3,493,325 2/1970 Roth 252/462 UX Penquite, Ballwin, all of Mo. 3.524.7218/1970 Stephens 252/462 X ['73] Assignee: Monsanto Company, St. Louis,Mo. Primary Examiner paul F shaver [22] Filed: Aug. 23, 1973 [21] Appi.No.: 391,167 [571 ABSTRACT A shrinkage resistant auto exhaust catalystcomprised lkemed Applicaflon Data of an alumina support and specifiedamounts of cop- [62] DlVlSiOn of Ser. No. 160,549. July 7, 1971, Pat.No. per, chromium d ifi rare earth compounds 378L406 and the use of thecatalysts under oxidizing conditions t d' b d d h d b 52 us. Cl.252/462; 252/465; 423/213 car c y mar ex [51] Int. Cl. B011 1l/06;B01j11/32 [58} Field of Search 252/462, 465 22 Claims- No Drawings SHRINKAGERESISTANT AUTO EXHAUST CATALYSTS This application is a division of ourapplication Ser. No. [60,549, filed July 7, 1971, now US, Pat. No. 3,78l ,406.

BACKGROUND OF THE INVENTION This invention relates to novel catalystsand means for preparing and using these catalysts. in particular, thepresent invention provides novel oxidation catalysts for removing carbonmonoxide and hydrocarbons from the exhaust of automotive engines with ahigh conversion efficiency coupled with unusual resistance to volumeshrinkage and weakening of the catalyst composite after exposure to hightemperatures. carbonaceous It is well known that when hydrocarbon fuelsare burned in automotive engines that combustion is incomplete. Thisapplies whether the engine be of the internal combustion type or otheralternative vehicular power sources. Substantial amounts of fuel areeither left unburned or are only partly combusted. This automotiveexhaust contains large amounts of carbon monoxide and hydrocarbons alongwith carbonaceeous residues (particulate form) among products ofincomplete combustion which are generally considered to be noxious. Inaddition, a fourth general category of pollutant is formed, termed NO,(NO and N Products of complete combustion are also present in largeamounts and consist of water and carbon dioxide. Remnants of airemployed to combust the hydrocarbon fuel include oxygen and nitrogen.Hydrogen is generally present along with components emanating from thecomposition of the hydrocarbon fuel utilized. For example, most presentday gasolines contain organic lead which decomposes to yield noxiouslead compounds.

The instantaneous composition of vehicular exhaust is a function of manyfactors, including parameters relating to engine design, and tuning, anddriving mode, as well as fuel composition. Thus, it is difficult tospecify a typical exhaust composition. Generally speaking, however, whenpresent day automobile engines are started cold, carbon monoxide levelsof about to about l5 volume percent, along with hydrocarbon levels ofabout 5,000 to about 15,000 parts-per-million are not unusual.

Carbon monoxide and hydrocarbon levels fall rapidly after engine startto levels of about 3 percent and 1,000 parts-per-million respectively inabout the first 100 seconds of engine operation. As the engine continuesto warm to normal operating temperatures, exhaust com positionscontaining about I to about 2 percent carbon monoxide and severalhundred parts-per-million hydro carbon are oftentimes observed withpresent day automobiles.

Exhaust compositions, even with warm engines, can deviate markedly fromthe representative values cited above. For example. poorly tuned engineswill yield higher emissions of incomplete combustion products. Sparkplug misfires can cause temporarily high pollutant levels as candeceleration driving modes.

Air pollution problems, particularly in major urban areas, haveincreased with the total automobile popula tion. Of the major classes ofair pollutants, automobiles contribute a substantial portion of thetotal with respect to carbon monoxide, hydrocarbons, nitrogen oxides,and particulate matter. Thus means of reducing substantially the levelsof these pollutants in vehicular exhaust have been sought.

Many proposals have been made concerning the use of catalytic convertersto accomplish oxidation of carbon monoxide and hydrocarbons in vehicularexhaust to carbon dioxide and water. Certain oxidation catalysts havebeen placed in specially designed containers located in vehicularexhaust trains. Supplemental air is oftentimes added to the exhaustprior to the special converter to ensure sufficient oxygen to promotecombustion. However, special carburetors or fuel injection systems canbe designed that allow vehicle operation at exceptionally leanconditions and that provide sufficient oxygen for catalytic combustionof carbon monoxide and hydrocarbons without the need for additionalsecondary air. In some cases, initial conversion efficiencies for carbonmonoxide and hydrocarbon oxidation with reported catalytic convertershave been quite good. After extended use, however, all presently knowncatalytic compositions lose effectiveness for one or more reasons.

The reason(s) for any particular catalyst failing to maintain anadequate conversion efficiency is not always known. It does appear,however, that successful catalyst compositions must be able to functionat low temperatures and also must retain adequate activity afterexposure at high temperatures. From the foregoing description ofrepresentative vehicle exhaust compositions, the low temperatureactivity requirement is obvious. A successful catalytic composite mustattain high conversion efficiency as quickly after engine start aspossible.

The same oxidation catalyst must retain all, or most, of its lowtemperature activity after exposure to very high temperatures. Forexample, temperatures of l,500F or higher may be encountered in highspeed driving, Even higher temperatures of l,800F or more can beencountered for brief periods of time with improperly operating engines,for example on the occasion of spark plug misfires.

In addition, a successful catalyst composition must retain an acceptabledegree of physical integrity after exposure to high temperatures. Forexample, a loss in volume of the catalyst bed can lead to by-passing orchannelling of exhaust gases resulting in lower conversion efficiencies.The potential void spaces in converters of certain designs can allowunrestricted movement of catalyst which may accelerate mechanicalattrition.

As mentioned, the precise reason(s) for failure of a particularcatalytic composite is oftentimes difficult to determine. One source ofdestabilization of aluminasupported catalytic composites is apparentlyrelated to the presence of specific actives. This effect has, to someextent, been recognized previously. For example, Smith et al in US. Pat.No. 2,422,172 recognized that oxides of chromium, manganese, iron,molybdenum and cobalt accelerate the thermal transformation of gammaalumin to alpha alumina. Smith, et al proposed reaction of activatedaluminas with certain alkaline earth compounds to counteract thistendency toward conversion of activated aluminas to more dense phases.Similar effects of metallic oxides on the alpha transformation ofalumina were reported by Wakao and Hibino {Nagoya Kogya GijussuShikensho Hokuku, Volume 1 1, 58895, 1962]. The authors studied 1 to 10%loadings of MgO, NiO, CuO, MnO Fe O TiO SiO BaO, BeO, Cr O ZrO CaO witha transition alumina.

The above mentioned oxides lowered the temperature required to formalpha-alumina (a mineralizing effect) as compared to the undopedalumina. Another recognition of the mineralizing effect of certainadditives with alumina is included in an article by Fink[Naturwissenschaften, Volume 2, 32, 1963]. Vanadia, V was found to lowerthe temperature for the alphatransformation of a transition aluminasubstantially.

The examples cited demonstrate that the balance of properties to beexpected from a catalytic composition is somewhat unpredictable. Forexample, a support which may be thermally stable in its own right is notnecessarily stable after addition of catalytic components (additives).Thus, alumina supports described herein may be stable to I,8()OF in theabsence of certain impurities or additives. Yet, when combined withcopper and chromium additives, both used herein, the same supports canconvert substantially to more dense phases, including alpha alumina. Thesupport phase transformations are oftentimes accompanied by massivevolume shrinkage, a factor not widely recognized.

Another potential source of instability with oxidation catalysts used intreating automotive exhaust is catalyst attrition. US. Pat. Nos.3,226,340 and 3,433,58l to Stephens et al, teach the use of first rowtransition metal oxideor lanthanide oxide-lamina followed by a copperoxide lamina for use in treating automotive exhaust. The Stephens et a1patents are directed toward providing an attrition-resistant autoexhaust oxidation catalyst. In their teachings, attrition-resistance isprovided by use of a catalyst consisting of an alumina support on whichis deposited an initial lamina of a first row transition metal oxide orlanthanide oxide followed by a copper oxide lamina. This is achieved byspecifically depositing the initial lamina component first and thenforming the cupric oxide component in a subsequent step. Stephens et alassert that the simultaneous deposition of the two additives gives bothpoor physical durability and a very high rate of attrition.

The catalysts of the present invention have distinctions and advantagesover the prior art, for example, over the catalysts of the Stephens etal patents cited above. The present catalysts contain a chromiumcomponent in a specified concentration range and oxidation state. Thechromium component is essential for imparting high activity. Theoxidation activity of the catalysts of the present invention containingin combination copper, chromium, and rare earths is superior to that ofcatalysts lacking chromium. High activity is essential to permitconformance to the rigid standards of the US. Clean Air Act of 1970 withrespect to allowable emissions of carbon monoxide and hydrocarbons. Toobtain the shrinkage resistance desired in the pres ent invention, it isnot necessary to deposit the rare earth component first to obtain aninitial lamina, but rather the rare earth, copper and chromium can bedeposited in any order. In fact, with proper care the three additivesmay be added simultaneously. The present invention requires properconcentrations of copper, particular rare earths, and chromium to obtainthe desired balance of initial activity, resistance to deactivation,shrinkage resistance, and other properties.

SUMMARY OF THE INVENTION The present invention involves an oxidationcatalyst for treating automotive exhaust, which couples good lowtemperature activity and high temperature stability with respect tovolume shrinkage, activity maintenance, and strength preservation. Thecatalyst utilizes a transition alumina support and specified loadings ofboth copper and chromium to give the required activity, along withcertain rare earths to control thermal volume shrinkage. It is essentialto have chromium, as well as copper, as copper alone does not producethe necessary low temperature activity. Rare earth loadings, asdescribed herein, are also essential as a copper and chromium containingcatalyst on transition aluminas is susceptible to excessive volumeshrinkage upon exposure to elevated temperatures.

The present invention is also directed to procedures for preparing suchcatalysts with relatively uniform distribution of the copper, chromium,and rare earth components on the support.

The present invention also involves a process for treating automotiveexhaust in the presence of sufficient oxygen to effect oxidation ofoxidizable components in said exhaust to non-noxious products over ashrinkage-resistant catalyst comprising a composite of a transitionalumina support, a copper-containing component, a chromium-containingcomponent, and a rare earth containing component. It is advantageous tohave sufficient oxygen present at all times to preclude reducingconditions which can lead to substantial catalyst deactivation. Reducingconditions are those in which there is less than a sufficient amount ofoxygen present to effect complete oxidation of the oxidizableconstituents, e.g. to effect oxidation of the hydrocarbon and carbonmonoxide present to carbon dioxide and water. In one embodimentsupplemental air is added to the exhaust upstream of the catalyst, toinsure sufficient oxygen.

DETAILED DESCRIPTION OF THE INVENTION The catalyst of the presentinvention is an oxidation catalyst comprising a transition aluminacontaining thereon, 2 to 15 weight parts copper component, 0.1 to 10parts chromium component, and 2 to 15 weight parts of rare earthcomponent, the rate earth component being further characterized ascontaining at least one weight part rare earth from the group consistingof lanthanum, neodymium or praesodymium or combinations thereof. Theforegoing and other weight part ranges herein are based on weight partsof metal per I00 weight parts A1 0 unless otherwise specified.

The present invention also is directed to a process for treatingautomotive exhaust in the presence of sufficient oxygen to effectcomplete combustion of the oxidizable components therein to non-noxiousproducts by contacting said exhaust with a catalyst comprising atransition alumina containing thereon 2 to 15 weight parts copper, 0.1to 10 weight parts chromium and 2 to l5 weight parts rare earth, therare earth component being further characterized as containing oneweight part rare earth from the group consisting of lanthanum, neodymiumor praesodymium or combinations thereof.

Each component of the catalytic composite is essential to achieving thenovel properties of the catalysts of the present invention. Rare earthsas used herein are essential in order to achieve stabilization againstvolume shrinkage. Rare earth, in the context of the present invention,is defined as including elements with atomic numbers 57 through 71. Ofthese elements, elements 57 through 60 are particularly valuable in theprocess of the present invention. Thus lanthanum, ce-

rium, praesodymium and neodymium are available in quantities sufficientto be of economic value in the present catalytic composites. Of the fourrare earths cited above, cerium can improve conversion efficiencies forcarbon monoxide with coppenchromium containing catalysts of the presentinvention, even after thermal aging at temperatures up to at leastl,800F. Hydrocarbon conversion efficiencies appear to be diminishedsomewhat from those conversion efficiencies obtained with onlycopper-chromium present, especially after high temperature aging.Cerium, however. imparts little, if any, shrinkage resistance.

Use of lanthanum, praesodymium or neodymium individually or incombination, on the other hand imparts excellent shrinkage resistance tothe copper-chromium catalysts of the present invention. With freshlyprepared catalysts, little activity difference is noted from compositescontaining only copper-chromium additives. However, with increasing rareearth loadings and after exposure to high temperatures, conversionefficiencies appear to suffer. Shrinkage resistance often improves withincreasing rare earth loading. Use of commonly available rare earthmixtures, containing about 50% cerium, gives results essentially likethose for lanthanum, praesodymium, or neodymium.

Thus, with respect to incorporation of the are earth component, abalance must be struck between desired shrinkage resistance andallowable activity loss after high temperature exposure. For thisreason, it is desirable that the rare content not exceed about l5 weightparts. Of the total rare earth employed, at least 1 weight part rareearth should be chosen from the group consisting of lanthanum,praesodymium or neodymium or combinations thereof. Cerium, if used,should ordinarily be present at no more than about weight parts.

A preferred range of rare earth loading with the catalytic composites ofthe present invention comprises about 2 to l0 weight parts total rareearth with about 1 to 6 weight parts rare earth from the groupconsisting of lanthanum, praseodynium, neodymium or combinationsthereof.

Copper and chromium, in combination, are necessary to obtain theexcellent conversion efficiencies of the catalysts of the presentinvention. Thus copper alone yields an alumina supported composite withinsufficient low temperature activity. Copper in combination with rareearths, especially cerium, yields improved low temperature performance.The latter combination, however, does not have the low temperatureactivity of composites containing copper and chromium, or copper,chromium and rare earth. The poorer conversion efficiencies in thepresent comparison are particularly notable with respect to hydrocarbonconversion, both with freshly prepared catalyst, and with catalysts thathave been exposed to high temperature. Furthermore, chromium-aluminacomposites, or rare earth-alumina composites have decidedly poorer lowtemperature activity than the preferred catalytic composites of thepresent invention.

In general, the copper loading used herein is in the range 2 to weightparts. However, we prefer to choose loadings which deposit the copperpredominantly as a highly dispersed copper aluminate, CuAl- 0 The stateof copper dispersion is determinable by a variety of techniques, forexample electron spectroscopy for chemical analysis (ESCA) [A. Wolberg,J.L.

Ogilvie, J. F. Roth, J. Catalysis 19 (I) 86-92 (l970)], K-edgeadsorption spectroscopy, or X-ray diffraction (XRD). We generally preferto employ the ESCA technique for its unique ability to determineoxidation state and chemical identity of elements of atomic number 3 orhigher at very low levels. Thus, ESCA is able to detect the oxidationstate and chemical form of copper present in copper-on-aluminacomposites at loadings of about 1 weight percent or greater. At such lowloadings, other techniques often fail to even detect the presence ofadditives on alumina supports, to say nothing of identifying thechemical form. For example, XRD is useful only when additives arepresent in a sufficiently high degree of crystallinity and/orsufficiently large crystal forms. In the copper containing composites ofthe present invention, crystalline copper phases are generally notobserved.

An especially preferred loading range of copper in catalysts of thepresent invention is about 4 to 10 weight parts copper. Within thisrange, on the supports of the present invention, the copper phaseconsists predominantly of copper aluminate as determined by ESCA. It isfelt that the above cited preferred range provides catalysts of optimumactivity and stability. With less copper, low temperature activitiesbecome unacceptable. With high copper loadings than about 10 weightparts, initial activities are very good, but sometimes only at theexpense of long term stability.

in addition to the restrictions cited previously as to rare earthloadings and copper loadings, the catalysts of the present inventionrequire specific amounts of chromium. We generally employ chromiumloadings of about O.l to 10 weight parts. Especially preferred is aloading range of about 0.5 to 7 weight parts chromium. In the catalystsof the present invention, the chromium is present predominantly in aplus six oxidation state as determined by ESCA. We have found that whenchromium is present predominantly in lower oxidation states, catalystswith significantly lower activities result.

Thus, preferred catalysts of the present invention comprise certaintransition aluminas containing thereon 4 to 10 weight parts copper, 0.5to 7 weight parts chromium, and 2 to 10 weight parts rare earth.Especially preferred combinations are further specified in that copperis present predominantly as a highly dispersed form of copper aluminateand chromium is present predominantly in a plus siz oxidation state,both chemical states being determined by ESCA measurements. Furthermore,of the total rare earth present, I to 6 weight parts should be selectedfrom the group consisting of lanthanum, praesodymium, neodymium orcombinations thereof.

The present invention utilizes a transition alumina as a support for thecopper, chromium and rare earth additives. By the term transitionalumina is meant an alumina other than alpha-alumina and also excludingcertain hydroxides of aluminum. Reference is made to Technical Paper No.10, second revision, from the Alcoa Research Laboratories. On page 9,various phases of alumina are enumerated. The following phases are notgenerally components in the catalysts of the present invention.

1. alpha alumina tri-hydrate Gibbsite 2. beta alumina tri-hydrateBayerite 3. Nordstrandite -Continued 4. alpha alumina mono-hydrateBoehmite 5. beta alumina mono-hydrate Diaspore 6. alpha alumina CorundumOf the above cited phases, the use of alpha alumina is definitely notdesired. The other phases may be present in small amounts but are notthe preferred starting materials for preparing the catalysts of thepresent invention.

A preferred support for the catalysts of the present invention thusconsists predominantly of a transition alumina. Although minor amountsof the phases listed above can be present, we prefer to prepare thecatalysts of the present invention with an alumina consisting of atleast 51% transition alumina. In other words, a preferred aluminasupport for the catalysts of the present invention consistspredominantly of one or more of the transition alumina phases identifiedby XRD as gamma, eta, theta, iota, chi or kappa. Especially preferredare supports consisting predominantly of gamma alumina or pseudo-gammaalumina.

In the context of the present invention by the term support is meant apredominantly alumina body which may contain thereon additives such ascopper, chromium and rare earth. Examples include particle forms ofalumina such as spheres, extrudates, hollow cylinders, star shapes, orothers, as well as alumina in the form of coatings on rigid underbodies,or thin shells of alumina in a rigid matrix. The geometrical forms ofalumina used in describing the catalysts of the present invention aremeant as illustrations only and are not meant to restrict the scope ofthe present invention.

The aluminas employed in the present invention can be furthercharacterized in terms of physical properties such as particle shape,particle size, surface area, pore properties and bulk density. Whenusing particle forms of transition alumina we generally prefer to employeither of two shapes, spheres or extrudates. These preferred shapes haveadvantages with respect to packing, mechanical attrition resistance andpossible cost advantages. Thus spheres represent an ideal case whereinno rough edges need be present which can abrade through rubbing togetherof packed assemblies of balls. Extrudates, especially those which havebeen tumbled to round the cylinder ends, also are a preferred particleform with respect to minimizing mechanical attrition.

The choice of particle size will of necessity depend on parametersrelating to engine and catalytic converter design. Thus a given enginewill function properly only up to a given back pressure. For a givenparticle size, this limits the depth of catalyst bed through whichexhaust gases are passed. As a practical compromise with engines andconverters of present-day design, we employ aluminas in the range ofsieve designation number 4 through sieve designation 16 (screen openingsbeing 0.187 inches and 0.0469 inches respectively).

With particle forms of transition alumina, we have found that superiorcatalysts result if sufficient surface area is present to distributecopper predominantly as well dispersed copper aluminate. In general,aluminas with surface areas of about 50 m lg or higher suffice, withranges of 200 to 400 m /g generally being used. (The BET method is usedto determine surface area, Brunauer-Emmet-Teller).

Again with particle forms of transition alumina, we have found thatcatalysts of the present invention display superior conversionefficiencies if the pore volume, measured by mercury intrusion at 2,500psig, of pores with diameters of 700 Angs. or larger is at least 0.18cc/g, and preferably at least 0.2 cc/g. The socalled macro-pore volumeapparently aids in funnelling reactants into the catalyst particleinterior resulting in a larger catalyst effectiveness factor.

For particle forms of transition alumina, we have found that bulkdensities of l0 to 40 lbs/ft provide superior bases on which to add theadditives of the present invention. The use of low bulk densitiesapparently is necessary to minimize heat-up time and thus beginconversion of oxidizable components as quickly after engine start as ispossible. With the exemplifications of the invention herein, a bulkdensity of at least 15 or 20 lbs/ft is ordinarily preferred to have therequired mechanical strength, thus giving a balance of strength andshort heat-up time, particularly in ranges of 20 to 30 lbs/ft. However,it may be feasible to utilize other means of improving mechanicalstrength, such as use of additional components, thereby removing therestriction of having a minimum bulk density of 15 or 20 lbs/ft.

The aluminas utilized herein can and frequently do have various amountsof other elements as impurities, such as, for example, silica and iron.lt is preferred that no more than 1 weight percent silica and 0.5 weightpercent iron (as Fe o be present, and, for optimum results, that thesilica be no more than 0.1 weight percent and the iron no more than 0.05weight percent. However, copper, chromium and rare earths will havebeneficial effects as taught herein in the presence of higher amounts ofimpurities than those of the aforesaid preferred ranges. Aluminas areavailable in which the impurities do not generally amount to more than1% of the material. When the term consisting essentially is used hereinwith respect to alumina or catalysts, it will be understood that theterminology includes designated materials but excludes components whichhave a deleterious effect upon fundamental properties of the materials,when present in amounts having such deleterious effects.

In preparing the catalysts of the present invention, the additivematerials can be added to the alumina support individually in any order,or in combinations. The object is to have all three types of additivesuniformly distributed.

We prefer to employ minimum solution impregnation techniques withparticle aluminas of the present invention. However, excess solutionprocedures are possible so long as care is taken to avoid non-uniformadditive deposition and to obtain the chemical states of dispersionheretofore described. In addition, co-forming of alumina and additivesis possible, and in some cases is preferable, for example to obtainfewer processing steps and better econimics of manufacture. For example,a valuable embodiment of the present invention involves co-forming ofalumina and rare earth. This may be accomplished by co-precipitations ofaluminum and rare earth hydroxides. Alternatively, the rare earth can beadded to already precipitated alumina gel. The resulting rareearth-aluminum hydroxide mixture can then be formed into desired shapesand sizes by techniques known to those skilled-in-the-art, for examplevia nodulation, extrusion or pelletting. Another modification ofco-gelling involves the so-called oil drop method. The carrier preparedby co-forming of alumina and rare earth can sometimes impart greatershrinkage resistance or strength to a catalyst prepared thereon than isobtained when the rare earth is deposited on a similar pre-formedalumina.

The calcined formed product can then be used to add not only thecopper-chromium additives emphasized in the present invention, but inaddition the rare earthalumina composite can be used as a carrier forother non-noble metals or for noble metals. In particular, such rareearth-alumina composites appear to be able to impart resistance to hightemperature induced volume shrinkage and mechanical strength loss.Specifically, the aforementioned rare earth-alumina composite appearsuseful for supporting additives selected from the listing V, Cr, Mn, Fe,Co, Ni, Cu, Zn, Mo, W, Ru, Rh, Pd, Ag, Re, Ir, Pt and imparting to suchcomposites thermal stability against volume shrinkage and mechanicalstrength loss.

With already formed alumina supports, minimum solution proceduressuffice. Aqueous solutions of commonly available salts are convenientlyused. For copper, the acetate and nitrate salts of divalent copper areespecially suitable although others can also be employed, for examplecuprous oxide. Copper nitrate is preferably deposited simply fromaqueous solution. When using copper acetate, solubility of the salt isenhanced by using about four or more moles of ammonia per mole ofcopper. Cuprous oxide is preferably deposited from ammoniacal tartaricacid solutions.

For chromium deposition in a single step, aqueous solutions of ammoniumdichromate are especially useful. If it is desired to co-impregnatecopper and chromium, aqueous solutions of copper nitrate with chromicoxide (CrO suffice. Likewise, chromium and rare earths can beco-impregnated from aqueous solutions of rare earth nitrate and chromicoxide.

Rare earths by themselves are conveniently deposited from aqueoussolutions of nitrate salts. Rare earth and copper can be co-impregnatedusing aqueous solutions of nitrates of rare earth and of copper.

The examples of impregnation procedures are not meant to be exclusive,rather illustrative. Thus other procedures may suffice to achievenecessary dispersions of the three required additives. Many proceduresdescribed in previous disclosures, however, are inadequate.

The impregnation procedures are intended to produce substantiallyuniform loadings of the additives. By substantially uniform is meantthat the additives are well dispersed and distributed throughout thesupport particles rather than just on the outer surface of individualparticles thereof and that the bulk thereof is at concentrations whichdo not differ greatly from the average concentration as measured byelectron probe microscopy. There may be some local high concentra'tions, such as in an ultra thin border region along particle edges, orin pockets in adjoining regions, but such regions or pockets willgenerally be less than 50 microns in thickness, and aften less thanmicrons in thickness, and will contain only a small fraction of thetotal additive. In addition, the different additives, e.g., rare earth,copper and chromium component will ordinarily be intermixed and will notbe present only in separate distinct regions or layers. Aside from theneed for good dispersion of actives to obtain proper activity,

catalytic composites containing nonuniform additive distribution oftenare less thermally stable. For example, with an iron-containing catalystof Example 7E, to follow, use of ferric nitrate resulted in selectiveadsorption of iron in regions nearest pellet external surfaces. Afterthermal aging of the catalyst of Example 7E, the outer pellet region wasdecidedly softer than the ironpoor interior regions. In fact, in crushstrength determinations, delamination or spalling was observed. On theother hand, a uniformly impregnated iron containing catalyst of Example7F, although possessing relatively poor over-all physical strength afterthermal aging, did not exhibit the delamination tendency of the 7Eexample.

The additives will be in oxidized states which in general will be in theform of oxides or aluminates, although other forms are possible. Whileit is preferred that the copper be predominantly in the form ofaluminate, copper oxide is a possible alternative form. Cerium dioxideis a common form of cerium, while lanthanum, neodymium and praesodymiumare known to form aluminates readily.

The impregnated support is preferably dried to drive the bulk of waterfrom the support prior to converting the metal additives to oxidizedform.

Conversion of the metal additives to final oxidized form is conductedconveniently by air calcination at temperatures above 350 C. Thepreferred calcination temperature is in the range of about 450 C toabout 750 C. For example, individual additives may have preferredcalcination conditions. We generally prefer to convert copper to itsoxidized form in the temperature range of 450 to 650 C, even morepreferably at temperatures of 500 to 600 C. Chromium on the other hand,is conveniently converted to oxidized form at 500 to 700 C, preferably500 to 650 C. Rare earths are conveniently converted to oxidized form attemperatures of 450 to 750 C depending on composition of the particularrare earth salt.

When combinations of additives are used, slightly different temperatureranges may be preferred, generally in the range of 550 to 650 C.However, the goal in calcination is to convert the salts employedsubstantially to their respective oxidized form.

After calcination, the catalysts of the present invention contain copperpredominantly as a copper aluminate as determined by ESCA. Chromium ispresent predominantly as plus six chromium as determined by ESCA.Chromium and copper are distributed essentially uniformly throughoutindividual pellets. Thus, electron probe microscopy indicates uniformdistribution of copper chromium throughout the interior of individualpellets. In some cases, very thin shells of higher copper-chromiumconcentrations are observed. With the preferred range of additiveloading, however, copper, chromium concentrations are everywhere withinthe broader ranges cited in the teachings herein. Furthermore, such edgeregions of higher additive concentration are very thin, for exampleabout 1 to 10 microns. Tests designed to determine if such admittedlythin boundary regions have different effects from bulk concentrationsindicate absence of the boundary yields equivalent to better catalystactivity. Rare earths likewise are distributed essentially uniformlythroughout the interior of individual pellets.

The oxidation catalysts described herein were evaluated with regard toconversion efficiency and thermal stability. Two types of conversionefficiency tests were employed. First, as has often been employedpreviously, we have used a steady state testing procedure whereinpercent-conversions of carbon monoxide and hydrocarbons are measuredwith catalyst beds heated to given temperatures. A plot ofpercent-conversion versus temperature is then constructed and thetemperature at which 50 percent conversion is achieved is determined.The so-called 50% temperature, light-off temperature. ignitiontemperature, is then one measure of how well a catalyst will perform ina cold start situation.

Steady state testing does not always adequately take into accountparameters which influence catalyst performance in cold start tests. Onefactor which is not accounted for properly in steady state tests in bulkdensity. Thus, we have observed that our preferred active system,prepared on a wide variety of selected alumina supports with varyingbulk densities, have nearly equivalent steady state activities. Yet,when heat-up properties are properly accounted for, a ranking of thecatalysts for effectiveness in cold start applications becomes apparent.Within the range of bulk densities for the aluminas required in thepresent invention, better cold start performance is obtained with lowerbulk densities, other factors being constant.

For this reason, we prefer to employ a transient activity test whichsimulates the first 4 minutes of the Federally-prescribed constantvolume sample (CVS) test (LA-4). it is well understood that catalystswhich fail to reach high conversion efficiencies in the first severalminutes of the test will fail present federal test standards.

The transient test procedure for catalysts reported herein duplicatescenter bed temperatures in representative CVS tests. Thus the influenceof catalyst heat-up properties is taken directly into account. Gascompositions and temperature ideally should be a function of time. inthe present transient test, however, the gas composition is chosen toreflect exhaust compositions achieved about 2 minutes into the test.Thus a gas blend containing (volume percent) CO 1 .6 O, 2.5 Propylene0.05 H 2. l balance N,

It will be noted that water levels are low in the present test and thatno C0, is present. Results with the cold start test describednonetheless correlate well with actual vehicle tests.

is preheated to 350C and passed over the catalyst bed, initially atabout room temperature. A sample representative of total gas compositionafter the catalyst bed is collected and analyzed. A %-rernaining valuefor CO and for total hydrocarbons is obtained which is directlyproportional to grams/mile emissions for these pollutants in actualCVS-tests. Results are reported both for freshly prepared catalysts, andfor catalyst which has been subjected to high temperature (24-hour airsoak at designated temperature).

The importance of adequately accounting for the influence of heat-up onconversion efficiency is further shown. A standard copper-chromiumformulation was employed using a procedure to be described in Example lto follow. Loadings were 5.63 weight parts copper, 3.83 weight partschromium per 100 weight parts transition alumina. Support properties offour supports employed in the present comparison include:

Test results with freshly prepared catalysts by steady state versuscold-state testing procedures are given below.

Test Procedure Steady State Cold Stsrt Example 50% Temperature inRemaining C0 HC CO NC A 222 308 $3 76 B 206 2B9 41 C 2l8 277 40 56 D 245277 28 3B The catalytic composites are listed in order of decreasingemissions as observed in actual CVS-tests. Thus, the lowest emissionswere achieved using the catalyst prepared on support D. Actual car testresults correlate well with the cold start data, whereas the steadystate data suggest quite a different ranking.

The catalysts of the present invention were also evaluated forresistance to volume shrinkage and deactivation at elevatedtemperatures. The effect of hydrothermal versus strictly thermal effectswas tested. With the catalysts of the present invention, test resultsincluding the presence of 10 15% water (as steam), in the temperaturerange 600 1,000 C, were observed to not alter substantially catalystrankings from those obtained from experiments without water. To expeditetesting, a straight thermal air soak was chosen for shrinkagemeasurements.

A 24 hour air soak at two or three temperatures was ordinarily employed.it was found that at certain temperatures, e.g. 1,700 F., thatcontinuing degradative effects could still be observed after 24 hours.However, by bracketing these temperature ranges with testingtemperatures where thermal effects were complete within 24 hours,reliable data was obtained. Ordinarily, sample sizes of S0 200 cc wereemployed. The larger sample sizes are preferred to minimize errors involume measurement.

Shrinkage is defined as (AV/Vo)) X (Original Volume Volume after) airsoak/original volume X 100 Crush strengths were measured on a ChatillonCompression Tester, Model LTCM. Data reported for spheres are forparticles just passing a sieve designation number 6 opening (0.132inch).

The invention herein is further illustrated by the following examples.

In the catalyst descriptions in the examples, the weight parts of metalsare given with respect to 100 weight parts of alumina support. it isunderstood that the basis is weight parts of support at the time offirst impregnation. Weight percent loss at 1,000 C (loi) is provided ineach example to enable computation of weight parts metal per 100 weightparts M EXAMPLE 1 Copper-chromium containing oxidation catalysts wereprepared on two transition aluminas having the following properties:

EXAMPLE 2 Shrinkage resistant oxidation catalysts were prepared onsupport B of Example l.

Ph sical form 5 X 8 sh here Y phases m a pigsdwummm w A rare earthnitrate mixture (Molycorp No. 480) was also pseudo-boehmite used inwhich the rare earth content (based on oxide) Suppm was apportioned asfollows:

Wt. loi' (1000C) 8.7 3.0 c 43% Surface area (m /g) 330 274 La 33% Porevolume (cc/g) Pr l3% Total 0.80 l .04 Nd 4.5% 700A radii 0.58 082 others1.5% 700A 0.22 0.22 Bulk density (lbs/ft") 32 27 Wt. sio, 0.l44 0,182Wt. Pep, 0.021 Wt. Na,0 0.12 Contaminants Maximum Typical Wt. i ion onignition after drying at 300C. Fqq, 0.07 0.01 gag. 5:0 2 .0 0.06 .5 0.25The prepaaration procedure employed is the so- MZ'o 0.5 0.02 calledminimum solution technique. a

. water insoluble 0.5 0. I The following general procedure was followed.Water adsorptivities of the supports were determmed- 100 Parts pp Athree step impregnation procedure was employed 1. solution volumes werecalculated to give about 6% excess liquid,

2. enough Cu (N0 3H O was dissolved to the volume computed in (1) togive 5.63 wt. parts copper per 100 wt. parts as received alumina.

3. a minimum solution impregnation was used to add the copper solutionto the support, for example by spraying onto support which wascontinuously tumbled.

4. the impregnated support was dried in a forced air drying oven at l20C to a constant weight.

5. the oven-dried material was calcined for 5 hours in a fixed bed in anair atmosphere. (If sufficient circulation through the bed is maintainedthe calcination time can be cut by as much a factor of 10.) A generalprocedure used was to place the oven dried material in mufflespre-heated to 150 C (to exclude water). Temperatures were then raised to500 C over a period of about 30-45 minutes, after which a 5 hour hold attemperature was begun.

6. The copper-containing material was then impregnated with aqueoussolutions of ammonium dichromate, (NH.),Cr 0 as described above. Thesolutions contained chromium sufficient to give 5.63 wt. parts copperplus 3.83 wt. parts chromium per 100 wt. parts support. After drying asdescribed above. the chromium was converted to oxidized form by 5 hourair calcination at 600 C.

The finished catalysts had copper and chromium disfollowing the generaloutline of Example 1 with drying and calcination steps betweenimpregnations. Rare earth was deposited first from aqueous solutions,followed by copper, followed by chromium. Calcination temperatures were600 C, 500 C, and 600 C respectively.

The catalysts of this example, along with compositions (in weight partsmetal per l00 parts support) consist of:

Sample Composition (wt parts) rare earth copper chromium A 2.04 5.633.83 B 4.16 5.63 3.83 C 6.38 5.63 3.83

Table l Shrinkage Cold Start, Remaining (AV/V,,) X [00 CO HC Rare EarthEx Wt. Parts l600F 1700F l800F Fresh l600F l700F l800F Fresh l600'Fl700'F 1800F 1A 0 5.0 10.3 21.9 35 37 38 50 51 56 98 1B 0 5.0 9.9 24.635 36 38 41 47 47 54 79 2A 2.04 3.3 6.4 I20 36 41 42 47 48 55 59 68 2B4.|6 3.8 5.7 10.0 35 40 39 43 49 54 56 63 2C 6.38 3.5 4.6 7.9 36 41 4348 53 57 63 ll The CO and HC refer to carbon monoxide and hydrocarbon inthe above and other tables herein.

Crush strength data on the catalysts of Examples 1 and 2 were asfollows:

by comparing the data of Example 3 with that of Example 2. Crushstrengths on sample C were 1 1.4 lbs force Example i 'g g flgf 800 onfresh catalyst and 10.7 after aging at 1,800" C. The

results indicate a greater need for the rare earths when :3 g g i3 3chromium is present in the catalyst in order to retain 2A 10 adequatephysical strength. 2B 8.3 5.9 4.0 3.7 2C 7.5 3.9 3.5 4.4 EXAMPLE 4 Adifferent type of transition alumina support was Results from Example 1demonstrate the need for [5 used to F' COPPeT'ChmmiUm mnfainingoxlqation stabilization against thermal degradative effects. Con-Catalysts alumma had followmg Propemes? version efficiencies with thecompositions of the exam- Physical form on emudate ple are nearlyconstant through l,700 F with respect 1/d-2 to removal of carbonmonoxide. Retention of hydrow p g fi H carbon activity is almost asgood. after L800 F aging, 20 Surface area 2/g however, a severe loss inconversion efficiency is ob- Pore volume /s) O 58 served for both carbonmonoxide and hydrocarbons. 2% A radii Shrinkage and loss of particlestrength, however, are 700 A. radii 0.19 excessive with the catalysts ofExample 1. Thus at af s g 007 1,800 F nearly a loss in volume in ExampleIB is 25 w F6263 o10l observed. In an actual catalytic converter, severebywt. 2 passing could occur.

In addition, the catalysts of Example I lose essen- A dual lmpl'egnatlonProcedure as descnbed "l E tially all or most of their physical strengthas measured ample 1 was p y to Prepare a Catalyst f g by crushingstrength after 1,800 F aging. The result in Parts PP R f P Chmm'um (bothactual converters could be massive mechanical abraas metals) P 100 P PPSion losses Copper and chromium dlstrlbutions and chemical The effect ofadding appropriate amounts of mixed 5mm were as descnbed Example rareearth is seen in Example 2. With an essentially equivalentcopper-chromium complosition, on the sup- EXAMPLE 5 port of Example lB,rare earth oadlngs increasing from zero to about 6 wt. parts reduce theshrinkage at The support of Exfimple 4 f usedfo Prepare Stabl- 1800 Ffrom 24.6% to 7.9%. A corresponding increase copper'cllromlum cfomammgoxldauon.catalysts' in crush strength at l800F is observed withincreasing A three i impregnation procedure equwalem to rare earth 10adin g 40 that described In Example 2, was employed to prepare threesamples. The catalysts of this example, had compositions (in weightparts metal per 100 weight parts EXAMPLE 3 support) as follows: SupportA of Example 1 was used to prepare a series of rare earth-coppercontaining oxidation catalysts. No 5 Composition chromium was added.Preparation procedures were as Sample rare earth pp Chwmium described 1nExample 2 through the copper-calcmation A 20 163 3 step. B 4.0 5.63 3.83C 6.0 5.63 3.83

w I The dispersion of copper and of chromium in finished Sample rarepans (as g catalysts was uniform throughout individual extrudatepellets. Copper was present predominantly as CuAl O g 2 222 asdetermined by ESCA. No crystalline copper C 1 containing phases weredetected by XRD. Chromium was present as +6 chromium as detennined byESCA.

The cerium component was, in part, present as crystal- The catalystsgave test results as listed in Table 2. line CeO as determined by XRD.

Table 2 Shrinkage Cold Start, Remaining (AV/V0) X 100 CO HC Rare EarthSample Wt. Parts l600F I700'F l800F Fresh l600F 1700F l800F Fresh 1600Fl700F 1800'F A 2.06 38 6] B 4.22 33 C 6.47 3.6 [0.6 35 49 56 62 74 89Table 3 Rare Shrinkage Cold Start, Remaining Earth (AV/V X I(J CO l-lCEx- Wt. I600 I700 I800 1600 I 700 l 800 1600 1700 I ample Parts F "F F2000 Fresh F F F 2000 Fresh F F 2 2000 4 U l.4 I01 I43 4i 43 67 98 S9 60I00 5A 2 0.5 2.0 8.9 35 45 49 87 53 63 73 5B 4 H13) l.l 5.3 37 45 SI 8257 67 79 I00 SC 6 0.4 0.4 5.4 35 5O 53 7I 58 76 85 I00 The example 4catalyst without rare earth has poor shrinkage properties at I800F.Addition of as little as 2 weight parts rare earth imp-ans markedlyimproved shrinkage resistance.

EXAMPLE 6 Samples of copper-chromium on alumina catalysts were preparedcontaining different individual rare earths, or the previously describedrare earth mixture. The alumina used had the following properties.

Physical form 5 X 8 mesh spheres loi (I000C) 5.6

Surface area (mlg) 287 Pore Volume (cc/g) Total 0.99 0-700 A 0.73 700 A0.26

Bulk density 290 XRD Phases pseudo-gamma The procedure of Example 2 wasemployed to obtain catalysts with 6.38 parts rare earth, 5.63 partscopper, and 3.83 parts chromium. Uniform distributions of the copper andchromium were obtained. Test results were as follows:

EXAMPLE 7 Various other additives were employed in combination withcopper-chromium containing catalysts. In each case, the new additive wasadded first, or was already present in the support used, prior tocopperchromium deposition. A description of the catalysts of thisexample follows.

A. The alumina support used in Example 1A was used to prepare acomposition containing 6.9 weight parts thorium, 5.63 weight partscopper, 3.83 weight Table 4 Shrinkage Cold Start, Remaining (AV/V IOO COHC Rare Earth 1600F I700F 1800F Fresh I600F I700F I800F Fresh I600FI700F I800F A Mixed 2.0 3 7 6.0 37 47 49 S4 59 71 74 BI B Cerium 2.4 6.92I.6 34 34 38 32 54 58 67 76 C Lanthanum 2.7 2.7 3.8 38 51 SI 57 59 7878 79 D Neodynium 2.0 2.6 4.3 36 49 47 59 75 77 82 E Praesodynium 2.0 29 3.9 39 48 52 58 62 75 80 78 Crush strength data on the catalysts ofexample 6 were as follows:

Example Fresh 1600 l 700 l 800 A 7.6 4.5 3.6 2. I B 6.9 5.5 7.5 6.2 C6.7 4.0 2.2 2.9 D 6.2 4.4 3.2 3.4 E 8.9 2.9 3.] 3.5

parts chromium. Thorium nitrate, Th(NO;,) was employed from aqueoussolution to deposit thorium. Thorium was converted to oxidized form byair calcination at 600 C. Copper and chromium were then added as inExample 1.

B. Barium nitrate, Ba(NO was used to prepare a composition containing 5weight parts barium, 5.63 weight parts copper, 3.83 weight partschromium, on an alumina support. Barium was converted to its oxidizedform by air calcination at 650 C. The alumina support used has thefollowing properties:

Physical form 5 X 8 mesh spheres XRD phases predominantly pseudo-gammaalso pseudoboehmite Wt. loi (I000C) 4.5 Surface area (m /g) 299 Porevolume (cc/g) Total .88 0-700 A .46 700 A .42 Bulk density (lbs/ft) 28Wt. SiO, .14 Wt. Fe O .037 Wt. Na o .28

When aqueous solutions of copper nitrate were used to impregnate thebarium-alumina composite, copper deposition was non-uniform. Most of thecopper added was deposited on the outer edge of individual pellets.However a substantially uniform copper deposition was achieved in thepresent procedure by employing ammonified aqueous solutions of copperacetate, Cu(C H H O. The mole ratio of Nl-l :Cu was 5:1. With 2Nl-l :Cua precipitate was observed. Preparation procedures from this point onwere as in example 1.

C. The support of example 8B was used to prepare a barium-aluminacomposite containing 5 weight parts barium via a different procedure.Aqueous solutions of Physical form 5 X 8 mesh spheres Copper chromiumcontaining catalysts were prepared using the procedure of example 1,5.63 weight parts copper, 3.83 weight parts chromium.

Test results of the catalytic composites of example 7 barium chloride,BaCl .H O, were used to add barium. 15 are included in Table 5.

Table 5 Shrinkage Cold Start, 1: (V/Vo) X 100 CO HC Weight 1600 l 7001800 1600 1700 l 800 1600 1700 1800 Ex. Additive part "F "F "F Fresh "F"F "F Fresh F "F F A Thorium 6.9 2.3 3.9 9.0 45 45 43 50 63 65 65 BBarium 5.0 3.6 5.0 7,8 49 57 78 59 76 87 98 C Barium 5.0 2.1 3.4 5.3 3953 74 65 69 79 89 D Manganese 5.0 10.8 28.6 31.2 35 45 69 77 66 97 99 EIron 5.0 13.0 21.2 24.1 37 47 72 87 54 78 100 100 F lron 4.0 8.2 18.8 3749 97 54 69 100 G1 1.5 4.4 48 96 93 G2 Silica 3 2.4 4.4 62 82 88 79 8996 G3 w 44 62 G4 Silica 3 1.4 4.3 61 92 86 74 89 92 G5 2.4 5.8 41 55 6854 68 99 G6 Silica 3 1.7 11.8 47 71 73 62 77 86 After drying andair-calcining at 1,600 F, unreacted barium was removed by water washing.The bariumalumina composite, after drying, was then used to preparecopper-chromium containing catalysts as in Example 7B, 5.63 weight partscopper, 3.83 weight parts chromium.

D. The support described in example 7B was used to prepare amanganese-alumina composite of 5 weight parts manganese. Aqueoussolutions of manganous nitrate, Mn(NO were used to add manganese. Afterdrying, manganese was converted to its oxidized form by air calcinationat 600 C. Copper and chromium were added then as in example 1, 5.63weight parts copper, 3.83 weight parts chromium.

E. The support of example 78 was used to prepare a 5 weight partiron-alumina composite. Ferric nitrate, Fe(NO .9H O, was employed fromaqueous solution for iron addition. Iron was converted to its oxidizedfrom by air calcination at 600 C. A uniform distribution of ironthroughout individual pellets was not obtained. Most of the irondeposited near the exterior of individual pellets.

F. The procedure of example 715 was duplicated except that ammoniumferricyanide, (NH Fe(C'N) was employed for iron addition. In thismanner, a uniform dispersion of 4 weight parts iron was obtained.

The iron-alumina composites of examples 7E and 7F were then used toprepare 5.63 weight parts copper- 3.8 3 weight parts chromium as per theprocedure of example l.

G. The effect of silica content was investigated using commerciallyavailable aluminas from Pechine-St. Gobain. Physical properties of thealumina-pairs utilized were similar except for silica content. Adescription of the aluminas follows.

The results of Table 5 demonstrate the uniqueness of the rare earthstabilizer employed in the present invention. Of the additives employedin Example 7, only thorium is effective in activity stabilizationcoupled with imparting shrinkage resistance. Thorium, however, is muchmore expensive than rare earths and, in addition, poses a radioactivityhazard.

Barium is an adequate stabilizer with respect to volume shrinkage. Useof barium, however, introduces an excessive activity penalty as shown inexamples B and C.

Manganese and iron, if anything, are de-stabilizers. Both appear topromote, rather than retard, shrinkage and loss of mechanical strength.

Silica, like barium, apparently interferes with the copper-chromiumadditives of the present invention. In the three sets of pairs, G1versus G2, G3 versus G4, G5 versus G6, the presence of silica leads toan inferior activity performance. ln addition, examples G1 through G6demonstrate the effect of employing supports lacking some of thedesirable attributes taught herein. For example, the high bulk densitiesof the G-series examples leads to poorer cold start performance.

EXAMPLE 8 Support Surface Area (mlg) A 256 B 302 C 137 D Steady State50% temperatures (Cl CO l-lC A 2i 2 283 B 212 282 C H4 277 D 2 l 4 292The example demonstrates the desirability of employing transitionaluminas with surface areas high enough to adequately disperse desiredamounts of additives.

EXAMPLE 9 The effect of support bulk density was investigaged. Supportswere chosen having good attributes, namely surface areas 200 m'lg,macropore volumes I 0.20 cc/g. Both supports of this example were in 5 X8 mesh spherical form.

Support Bulk density (lbs/ft) The procedure of Example 1 was used toprepare copper-chromium oxidation catalysts containing 5.63.

weight parts copper and 3.83 weight parts chromium per 100 weight partssupport.

Test data were as follows on the fresh catalyst:

Cold Start Remaining CO HC 41 65 35 50 The cold start rest results showsubstantially higher emissions for the catalyst on the 39 lb/ft aluminacompared to 32 lbs/ft. It is desirable to use as low a built density asis consistent with adequate mechanical strength.

EXAMPLE ID B. Mixed rare earth nitrate and copper nitrate wereco=impregnated from aqueous solution to yield 6.47 weight parts rareearth, 5.63 weight parts copper. After calcinetion at 600 C each majoradditive was uniformly distributed throughout individual pellets. Copperwas present predominantly as copper aluminate and no copper-containingphases were detected by XRD. The rare earth-copper composite was thenutilized to add 3.83 weight parts chromium as in Example 1. The supportused in the present example had the following properties:

Plt slcal X D phases Wt. loi (lOOO'C) 5 X 8 mesh spheres predominantlypseudo-gamma, glso pseudo-boehmite Surface area (111%) 208 Pore volume(cc/g) Total 0.93 O=-700 A .75 700 A .l8 Bulk density (lbs/Ft) 30 It wasfound desirable to employ a heat treatment with the alumina of thepresent example prior to deposition of copper-rare earth. Otherwise, anexcessive amount of fines resulted after calcination. The extra heattreatment step, however, is not generally necessary; for example, it wasnot necessary with the support described in Example 6.

C. 1. Another so-impregnation procedure was employed to deposit rareearth and chromium on the transition alumina described in Example 73. Anaqueous solution of chromic oxide, CrO,-,, and rare earth nitratemixture number 480 from Molycorp was utilized to obtain 6.47 weightparts rare earth, 3.83 weight parts chromium. After drying, calcinationwas conducted at 600 C. Copper was then added at a 5.63 weight partloading using an aqueous solution of copper nitrate. Copper wasconverted to its oxidized form by air calcination at 500 C. Each majoradditive was distributed essentially uniformly throughout individualpellets. Copper was present predominantly as copper alumimate and nocrystalline copper-containing phases were detected by XRD.

2. When co-impregnation from an aqueous solution of rare earth nitrateand ammonium dichromate was attempted, a much more non-uniform additivedistribution was observed.

D. Still another means of co-impregnating the additives of the presentinvention is described. Copper and chromium were added to the transitionalumina described in Example lA. Amounts of copper and chromium werechosen to yield 5.63 weight parts copper and 3.83 weight parts chromium.

1. An attempt was made to employ an aqueous solution of copper nitrateand ammonium dichromate. Cosolubility of the two salts was notsufficient to prepare the desired copper-chromium loading.

Likewise, co-solubility was insufficient when copper acetate was used inplace of copper nitrate.

2. A concentrated ammonium hydroxide solution of copper nitrate andammonium dichromate was prepared with gentle heating being required. Theimpregnated support was dark green at first. However, while air dryingprior to placement in a l20 C drying oven, at violet-purple powderysubstance formed on the surface of the support. A substantial portion ofthe additives was lost.

3. Chromium nitrate, Cr(NO .9 H O, was observed to adsorb only on theexterior edge of individual pellets. For this reason, when attempting toemploy common solutions of nitrates of chromium and copper, am

monified solutions were tried. Purple sludge, possibly 5 containing ahydroxide of chromium, resulted.

4. None of the previously described attempts were successful inpreparing uniform disperions of copper and chromium throughco-impregnation. A successful procedure was evolved wherein a commonaqueous so lution of CrO and Cu(NO .3l-l O was prepared. After minimumsolution impregnation, the support particles were bright mustard incolor. After drying, and air calcining at 600 C, uniform distributionsof copper and chromium were observed. Copper was present predominantlyas copper aluminate, and no crystalline copper-containing copper phaseswere detected by XRD.

Evaluation results on some of the catalysts of Exam- 2 ple are reportedin Table 6.

The data clearly shows the necessity of having chromium in the catalyst.

EXAMPLE l2 The effect of exhaust gas composition with respect to overalloxidation-reduction stoichiometry was investigated. The test employedinvolved cycling gas compositions between feed-streams containing 0and/or CO. ln Test A, the feed compositions were designed to sim ulateconditions wherein gas compositions varied between overall reducing(feed l) to overall oxidizing (feed 2). Test B, on the other hand,varied the O .C0 ratio but at all times had a net overall oxidizingcomposition. The extremes of O :CO composition in the two feedstreams ofTest B were chosen to simulate relatively lean and relatively richexhaust gas compositions present in CVS-vehicle tests (LA-4 test) usingvehicles equipped with secondary air injection. In Test B, the exposuretimes for feeds l and 2 are representative of the proportion of timeeach gas composition is encountered in vehicle tests.

Table 6 Shrinkage Cold Start, Remaining V/Vo) X 100 CO HC Example l600Fl700F l800F Fresh I600F l 700F l 800F Fresh l 600F l 700F l 800F ll A-l2.3 6.1 36 46 55 53 66 79 ll A-Z 4.0 8,2 36 45 51 52 64 74 ll B 2.0 3.76.4 38 43 48 53 55 65 72 77 ll Cl 2.0 6.0 6.0 4l 48 49 51 57 6B 7] Thedata of Table 6 demonstrate that the low shrinkage catalysts of thepresent invention can be made in a variety of ways. Order ofimpregnation, in itself, has no significant effect. Among importantparameters to control, on the other hand, are additiveloading, andstate-of-dispersion.

EXAMPLE 1 l Catalyst composites were prepared containing varying amountsof copper, and copper with chromium, on the alumina support of Example1A. The procedure of Example 1 was used, with Cu(NO;,) .3H O being usedfor the copper impregnation, and (NH, Cr O for the chromiumimpregnation. The copper impregnation was followed by calcining at 500C, and the chromium impregnation by calcining at 500 C, and the chromiumimpregnation by calcining at 600 C. Cold start results on the freshlyprepared catalysts were as follows: 55

Table 7 Cold Start Remaining (Wt. pts/hundred) CO HC Copper Cr Catalyst(Wt. pts/hundred) The testing conditions of the two cyclical testsemployed in the present test are further specified.

The effect of the two different cyclical exhaust environments oncatalysts containing the components of the present invention, namelycopper, chromium and rare earth was followed by measurement of 50%conversion temperatures for carbon monoxide and for hydrocarbons.Results are given in Table 8.

Table 3 Catalyst Support A Steady State SOP'v-Temperature (C) No.Additives Frill. density mesh Sift? Test A Test B lwtparts) ribs/ft!initial 400 hrs. lnitial 400 hrs Cu (r RE* CO HC CO HC CO H: CO HC A5.63 w 47 R X i4 140 335 225 360 B 5.63 3.83 47 5 X ii 220 290 230 365 C5.63 3.83 32 5 X 8 231 275 230 370 D 5.63 32 5 X 8 245 395 285 415 E5.63 32 it i4 250 290 265 365 F 5.63 3.83 2.04 32 5 4 8 225 285 230 300'Molycorp rare earth nitrate mixture No 480 It will be noted that twodifferent types of spherical transition aluminas were utilized in thepresent example, one with a high bulk density (47 lbs/ff), another witha lower bulk density {32 lbsfft in addition, each was utilized in twodifferent size ranges, namely 5 X 8 mesh and 8 X 14 mesh.

Catalyst preparation procedures were accomplished as described inprevious examples employing separate impregnation steps for eachadditive.

The data show that coppenchromium containing oxidation catalysts suffersubstantial activity losses when exposed to cyclicaloxidation-reduction. Thus both catalysts B and C deactivatedsubstantially with respect to hydrocarbon conversion. This is shown byan increase in hydrocarbon 50% Temperature of 75 C and 95 C forcatalysts B and C respectively. Catalyst A, containing copper but nochromium, did not exhibit the high level of deactivation. In any case,the activity levels of the copper only or the copperchromium containingcomposites are both unacceptable after 400 test hours.

When gas compositions are kept over-all oxidizing, yet cyclicallyvarying in O :CO ratio, a different picture results. Thus catalyst F,containing copper, chromium and rare earth deactivated only slightlyafter 400 hours representing l ,200 cyclical changes in gas composition.The superior activity of copper chromium containing compositions is nowclearly apparent over compositions containing only copper. Theperformance of copper only samples D and E is poor, particularly aftercyclical aging. In addition, the data for D, E again points out thatsmaller particles give better conversion effi ciencies. This isparticularly noticeable for hydrocar bon conversion.

The data of Example 1?. demonstrates the wisdom of utilizing thecatalysts of the present invention with sufficient oxygen to maintain anover-all oxidizing exhaust composition. Multiple exposure of thecatalysts of the present invention to alternately oxidizing and reducingconditions can result in serious deactivation. We have observed acorrelation with catalysts of the present in vention between activitylevel and chromium oxidation state as determined by ESCA. It may be thatthe efficacy of maintaining over-all oxidizing exhaust stoichiomitriesis related to maintaining chromium in a preferred high oxidation state.In any event, it is advantageous to have oxygen present in exhaust inexcess of that required for oxidation of combustible exhaust componentsin order to maintain the catalysts of the present invention in a highlyoxidized form", specifically, multiple exposure of the catalyst tomultiple reducing conditions is to be avoided.

As discussed above, copper, rare earth and chromium are all essentialcomponents of the catalyst of the present invention. It has, however,been found that the presence of rare earth makes it possible to achievea particular level of hydrocarbon conversion activity with a loweramount of chromium than would be required in the absence of rare earth.There are advantages to maintaining low chromium contents, to the extentconsistent with desired activity and the ranges taught herein, aschromium tends to have an adverse effect upon physical properties suchas crush strength.

We claim:

1. A catalytic oxidation composite effective at elevated temperature andparticularly resistant to volume shrinkage and other thermal degradationconsisting essentially of an alumina which is a transition alumina andother than alpha alumina and having dispersed therein loadings ofcopper, chromium and rare earth components, with the loadings of thesaid components being intermixed and well dispersed throughout thealumina rather than limited to separate regions of the alumina. and withthe loadings being present, on a metal basis per parts Al O basis, inamounts of 2 to 5 weight parts copper, 0.1 to 10 wt. parts chromium, andl to l5 weight parts total rare earths, with at least 1 weight part ofthe rare earth being selected from the group consisting of lanthanum,neodymium, praseodymium, and mixtures thereof, and with the copper beingpredominantly well dispersed copper aluminate as determined by ESCA andwith the alumina used to prepare the composite having surface area of atleast 50 m lgram so as to provide sufficient surface for the copper tobe weil dispersed.

2. The catalytic composite of claim 1 characterized in that thetransition alumina has a macropore volume of at least 0.18 cc/g.

3. The catalytic composite of claim 1 characterized in that thetransition alumina has a specific surface area of at least 200 m /g.

4. The catalytic composite of claim 1 characterized in that thetransition alumina has a bulk density in the range of about 10 to 40lbs/ft.

S. The catalytic composite of claim 1 further characterized in that thesilica content therein as impurity is no greater than 1 weight part per100 weight parts alurnma.

6. The catalytic composite of claim 1 further characterized in that theiron content thereof as impurity is no greater than 0.5 weight parts per100 weight parts alumina.

7. The composite of claim 1 in which the metals are present in amountsof 4 to 10 weight parts copper, 0.5 to 7 weight parts chromium, and 2 to10 weight parts rare earth with 1 to 6 weight parts being selected fromthe group consisting of lanthanum, neodymium, praesodymium and mixturesthereof.

8. The composite of claim 1 in which the amounts of silica and ironpresent thereon as impurities are no greater than I weight part and 0.5weight part respectively per 100 weight parts alumina.

9. The composite of claim 1 in which additive loadings are welldispersed and substantially uniformly distributed in the alumina.

10. The composite of claim 1 in which the rare earth component comprisesno more than l parts by weight cerium.

11. The method of preparing an oxidation catalyst for treatment ofautomobile exhaust which comprises substantially uniformly impregnatinga transition alumina with solutions of soluble copper, chromium, andrare earth compounds and calcining at high temperatures to convert thecompounds to active oxidized forms and produce an active catalystcontaining substantially uniform dispersions of the aforesaid compounds,the compounds being used in amounts to provide 2 to weight parts copper,0.5 to 7 weight parts chromium, and l to 15 parts rare earth, with atleast 1 wt. part rare earth being selected from the group consisting oflanthanum, naodymium, praesodymium and mixtures thereof, all on a metalbasis, per 100 parts M 0 12. The method of claim 11 in which thecatalyst is calcined in air at temperatures of 550 to 650 C.

13. The process of claim 11 in which the alumina is impregnated byminimum solution technique from dilute aqueous solutions of additivesalts.

14. The method of claim 11 wherein aqueous solutions of copper nitrateare employed to deposit copper.

y 15. The method of claim 11 wherein aqueous solutions of ammoniumdichromate are used to deposit chromium.

16. The method of claim 11 wherein ammoniacal solutions of copperacetate are used to deposit copper, the amount of ammonia being at least2 moles NH, per mole of copper.

17. The method of claim 11 wherein aqueous solutions of rare earthnitrates and copper nitrate are used to co-impregnate copper and rareearth.

18. The method of claim 11 wherein aqueous solutions of copper nitrateand chromic oxide are used to co-impregnate copper and chromium.

19. The method of claim 11 wherein aqueous solutions of copper nitrate,chromic oxide and rare earth nitrate are used to co-impregnate copper,chromium and rare earth.

20. The method of claim 11 wherein aqueous solutions of rare earthnitrate and chromic oxide are used to co-impregnate rare earth andchromium.

21. The method of claim 11 in which the catalyst is impregnated byminimum solution technique from dilute aqueous solution of copper andrare earth compounds selected from the group consisting of acetates andnitrates of copper and rare earth, cuprous oxide, and dilute aqueoussolutions of chromic compounds selected from the group consisting ofchromic oxides and dichromates.

22. The method of claim 11 in which the alumina is dried by heating attemperatures of to C prior to calcining at temperatures in the range of450 to 750 C.

l 1 i i k

1. A CATALYTIC OXIDATION COMPOSITE EFFECTIVE AT ELEVATED TEMPERATURE ANDPARTICULARLY RESISTANT TO VOLUME SHRINKAGE AND OTHER THERMAL DEGRADATIONCONSISTING ESSENTIALLY OF AN ALUMINA WHICH IS A TRANSITION ALUMINA ANDOTHER THAN ALPHA ALUMINA AND HAVING DISPERSED THEREING LOADINGS OFCOPPER, CHROMIUM AND RARE EARTH COMPONENTS, WITH THE LOADINGS OF THESAID COMPONENTS BEING INTERMIXED AND WELL DISPERSED THROUGHOUT THEALUMINA RATHER THAN LIMITED TO SEPARATE REGIONS OF THE ALUMINA, AND WITHTHE LOADINGS BEING PRESENT, ON A METAL BASIS PER 100 PARTS AL2O3 BASIS,IN AMOUNTS OF 2 TO 15 WEIGHT PARTS COPPER, 0.1 TO 10 WT. PARTS CHROMIUM,AND 1 TO 15 WEIGHT PARTS TOTAL RARE EARTHS, WITH AT LEAST 1 WEIGHT PARTOF THE RARE EARTH BEING SELECTED FROM THE GROUP CONSISTING OF LANTHANUM,NEODYMIUM, PRASEODYMIUM, AND MIXTURES THEREOF, AND WITH THE COPPER BEINGPREDOMINANTLY WELL DISPERSED COPPER ALUMINATE AS DETERMINED BY ESCA ANDWITH THE ALUMINA USED TO PREPARE THE COMPOSITE HAVING SURFACE AREA OF ATLEAST 50 M2/GRAM SO AS TO PROVIDE SUFFICIENT SURFACE FOR THE COPPER TOBE WELL DISPERSED.
 2. The catalytic composite of claim 1 characterizedin that the transition alumina has a macropore volume of at least 0.18cc/g.
 3. The catalytic composite of claim 1 characterized in that thetransition alumina has a specific surface area of at least 200 m2/g. 4.The catalytic composite of claim 1 characterized in that the transitionalumina has a bulk density in the range of about 10 to 40 lbs/ft3. 5.The catalytic composite of claim 1 further characterized in that thesilica content therein as impurity is no greater than 1 weight part per100 weight parts alumina.
 6. The catalytic composite of claim 1 furthercharacterized in that the iron content thereof as impurity is no greaterthan 0.5 weight parts per 100 weight parts alumina.
 7. The composite ofclaim 1 in which the metals are present in amounts of 4 to 10 weightparts copper, 0.5 to 7 weight parts chromium, and 2 to 10 weight partsrare earth with 1 to 6 weight parts being selected from the groupconsisting of lanthanum, neodymium, praesodymium and mixtures thereof.8. The composite of claim 1 in which the amounts of silica and ironpresent thereon as impurities are no greater than 1 weight part and 0.5weight part respectively per 100 weight parts alumina.
 9. The compositeof claim 1 in which additive loadings are well dispersed andsubstantially uniformly distributed in the alumina.
 10. The composite ofclaim 1 in which the rare earth component comprises no more than 10parts by weight cerium.
 11. The method of preparing an oxidationcatalyst for treatment of automobile exhaust which comprisessubstantially uniformly impregnating a transition alumina with solutionsof soluble copper, chromium, and rare earth compounds and calcining athigh temperatures to convert the compounds to active oxidized forms andproduce an active catalyst containing substantially uniform dispersionsof the aforesaid compounds, the compounds being used in amounts toprovide 2 to 15 weight parts copper, 0.5 to 7 weight parts chromium, and1 to 15 parts rare earth, with at least 1 wt. part rare earth beingselected from the group consisting of lanthanum, naodymium, praesodymiumand mixtures thereof, all on a metal basis, per 100 parts Al2O3.
 12. Themethod of claim 11 in which the catalyst is calcined in air attemperatures of 550* to 650* C.
 13. The process of claim 11 in which thealumina is impregnated by minimum solution technique from dilute aqueoussolutions of additive salts.
 14. The method of claim 11 wherein aqueoussolutions of copper nitrate are employed to deposit copper.
 15. Themethod of claim 11 wherein aqueous solutions of ammonium dichromate areused to deposit chromium.
 16. The method of claim 11 wherein ammoniacalsolutions of copper acetate are used to deposit copper, the amount ofammonia being at least 2 moles NH3 per mole of copper.
 17. The method ofclaim 11 wherein aqueous solutions of rare earth nitrates and coppernitrate are used to co-impregnate copper and rare earth.
 18. The methodof claim 11 wherein aqueous solutions of copper nitrate and chromicoxide are used to co-impregnate copper and chromium.
 19. The method ofclaim 11 wherein aqueous solutions of copper nitrate, chromic oxide andrare earth nitrate are used to co-impregnate copper, chromium and rareearth.
 20. The method of claim 11 wherein aqueous solutions of rareearth nitrate and chromic oxide are used to co-impregnate rare earth andchromium.
 21. The method of claim 11 in which the catalyst isimpregnated by minimum solution technique from dilute aqueous solutionof copper and rare earth compounds selected from the group consisting ofacetates and nitrates of copper and rare earth, cuprous oxide, anddilute aqueous solutions of chromic compounds selected from the groupconsisting of chromic oxides and dichromates.
 22. The method of claim 11in which the alumina is dried by heating at temperatures of 60* to 150*C prior to calcining at temperatures in the range of 450* to 750* C.